This application claims priority under 35 U.S.C. xc2xa7119 and/or 365 to patent application Ser. No. 0100211-2 filed in Sweden on Jan. 26, 2001, the entire content of which is hereby incorporated by reference.
The present invention relates to a milling insert and a milling tool, used especially for roughing operations, wherein the milling insert has main cutting edges and secondary (wiper) cutting edges.
U.S. Pat. No. 4,966,500 shows a milling cutter having hexagonal cutting inserts. Each cutting insert has a main cutting edge, an end cutting edge and a radially internal cutting edge. The radially internal cutting edge is intended to cut during ramping of the workpiece.
U.S. Pat. No. 4,632,607 shows a square milling Insert having four pairs of cutting edges and having protruding secondary cutting edges (i.e., wiper edges). The milling tool produces perpendicular corners in the workpiece.
The main cutting edges of those prior cutting inserts are particularly sensitive to impacts and vibrations. For example, FIG. 4A depicts a cutting insert 100 according to U.S. Pat. No. 4,632,607 during a milling operation performed on a workpiece W, with a feed direction F. The insert includes main cutting edges 102A, 102B, 102C, 102D which are associated with respective secondary cutting edges 104A, 104B, 104C, 104D. In FIG. 4A the milling is being performed by the active main edge 102D and the active secondary edge 104D associated therewith. During the milling operation, the secondary edge 104D can travel off an edge 106 of the workpiece (see FIG. 4B). When that occurs, a built-up spring force that may exist in the milling machine can press the insert downwardly, whereupon the inactive main cutting edge 102A disposed adjacent to the active secondary cutting edge could impact against the workpiece, as shown in FIG. 4B, possibly with enough force to become chipped as a result.
An object of the present invention is to provide a milling insert and a milling tool mainly for roughing operations, which are less sensitive to impacts and vibrations.
Another object of the present invention is to provide a durable milling insert.
Still another object of the present invention is to provide a milling insert that provides impact protection for the main cutting edges in relation to the workpiece.
The present invention relates to a milling insert comprising a body having upper and bottom surfaces interconnected by an edge surface structure. A transition between the upper surface and the edge surface structure forms a main cutting edge structure comprised of a plurality of identical main cutting edges. The body further includes a plurality of protruding portions. Each protruding portion is disposed at a corner toward which two of the main cutting edges converge. Each protruding portion forms a secondary cutting edge disposed outside of an intersection of imaginary extensions of the two main cutting edges. The secondary cutting edge is joined to a first of the two main cutting edges by a transition edge. The edge surface structure forms a plurality of clearance surfaces for respective ones of the main cutting edges. Each clearance surface includes a first portion extending from a respective main cutting edge, a second portion extending from the first portion, and a third portion extending from the second portion. The first and second portions together form a generally convex profile.
The invention also pertains to a tool which includes a holder that carries a plurality of the milling inserts. The holder is rotatable about an axis. A plane which is oriented perpendicular to the axis and which contains a transition of a generally concave clearance surface associated with an axially forwardmost inactive main cutting edge, is oriented axially forwardly of such axially forwardmost inactive main cutting edge.